A lamp reflecting mirror, especially a car lamp reflecting mirror such as a head lamp, a fog lamp, or the like, uses an electric-light bulb of a very high luminance. Because the lamp reflecting mirror must endure high heat generated from a filament in use, a molding composition containing, as a base resin, a thermosetting resin such as unsaturated polyester or the like, or a heat-resisting thermoplastic resin such as polyether-imide, polyether-sulfone, polyphenylene-ether, heat-resisting polycarbonate, or the like, is used as a substrate for the reflecting mirror.
Although a polyester molding composition containing an inorganic filler such as calcium carbonate or the like in a glass fiber-reinforced unsaturated polyester molding composition is well known, use of a thermoplastic resin to form a reflecting mirror by a method such as injection molding or the like is advantageous from the viewpoints of reduction in the weight of the lamp, rationalization of productivity, and so on, so that the realization thereof is demanded.
Although the base resin to be used for a lamp reflecting mirror requires a heat resisting property to endure a heating temperature at the time of lighting of the lamp, if a thermoplastic resin composition is used for a lamp reflecting mirror, there has been such a problem that the reflecting mirror expands by the rise of heat in the lamp chamber at the time of lighting of the lamp so that the optical axis moves to make it impossible to obtain sufficient luminous intensity distributing performance because of the large linear expansion coefficient.
If a polyphenylene sulfide resin is used as the base resin, the heat resisting property is improved and the aforementioned problem in luminous intensity distributing performance at the time of lighting of the lamp can be solved. However, there is still a problem in the form retaining characteristic at the time of adjustment of the optical axis because the stiffness is still low.
On the other hand, a technique by which a glass fiber-reinforced polyphenylene sulfide molding composition is used so that a lamp reflecting mirror is obtained by injection molding is proposed.
The molding composition containing glass fiber is improved in the stiffness of the material to thereby improve the form retaining characteristic at the time of adjustment of the optical axis but is inferior in surface smoothness. Accordingly, it has been necessary that an undercoat layer is applied for improvement of the reflecting characteristic before the formation of a metal coating such as an aluminum coating or the like in order to make the metal coating deposit well.
In the undercoat layer, however, not only a problem arises such that the heat resisting property is lowered because the undercoat layer has a bad influence on heat resistance of the metal coating surface but also another problem arises such that good luminous intensity distributing performance cannot be obtained particularly in a level-difference reflecting mirror in which luminous intensity distribution is controlled only by the reflecting mirror, because an undercoat agent is reserved in level difference portions so that irregular reflection occurs. Furthermore, from the viewpoints of the influence of an organic solvent contained in an undercoat waste on environmental health upon application of an undercoating, improvement of productivity, and so on, there is demanded the appearance of a novel lamp reflecting mirror in which a sufficient light reflecting characteristic (surface smoothness) can be obtained without application of any undercoat layer and in which the aforementioned heat resisting property, luminous intensity distributing performance (dimensional stability) and form retaining characteristic can be satisfied at the same time.
Particularly in the high-strength lamp reflecting mirror of this type, when distortion occurs in the reflecting mirror surface, the reflecting mirror surface is roughened by the distortion so that light emitted from the electric-light bulb cannot be controlled accurately. Therefore, because a problem arises in the generation of a blinding flash to an oncoming vehicle, an unsatisfactory luminous intensity distributing standard, and so on, it is required that 1N. the reflecting mirror has an optically highly accurate reflecting surface. Therefore, it is necessary to develop a thermoplastic resin molding material by which a reflecting mirror substrate having excellent heat resisting property, dimensional stability, surface smoothness and stiffness can be provided.